This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The transcription factors Oct4, Sox2 and Nanog are key in embryonic stem cell identity and reprogramming. Insight into theirs partners and post-translational modifications should illuminate how the pluripotent state is established and regulated. Our aim is to identify Oct4, Sox2 and Nanog-binding partners from human ESC extracts by a series of pull-down assays, and subsequent analysis by multidimensional protein identification technology (MudPIT) followed by stringent data filtering. In addition, we will also identify various post-translational modifications of Oct4 and Nanog by MudPIT technology.